1. Field of the Invention
The present invention relates to a coupling device such as a link rod used as a suspension link for automobiles, an engine mount which couples an automobile engine and a chassis, or the like.
2. Description of Related Art
The well-known coupling devices include a link rod shown by way of example in FIGS. 1 to 3. As best shown in FIGS. 1 to 3, the link rod comprises an elongated plate-like rod body 100 made of a synthetic resin. The rod body 100 has a cylindrical end portion 101 formed integrally at each end thereof. Each cylindrical portion 101 has a cylindrical joint piece 102 disposed therein. A rubber-made elastic joint piece 103 is formed between the cylindrical portion 101 and joint piece 102. The rod body 100 consists of a plate member 105 ribbed as indicated with a reference numeral 104 to reinforce the plate member 105 and hence the rod body 100 as a whole. The ribs 104 are formed in two pairs, upper and lower, on the plate member 105. The ribs 104 in each pair extrude in opposite directions orthogonal to the plate member 105. They extend along the longitudinal perimeters, upper and lower, respectively, of the plate member 105 as well as between the cylindrical portions 101.
If such a link rod is used as a suspension link of an automobile, the rod body 100 or any other synthetic resin-made portion thereof is likely to be broken by a stone or the like bounded from the road surface by the wheel of the running automobile or by a curb with which the rod body 100 will possibly collide when the automobile comes too close to the sidewalk. If the rod body or cylindrical end portion is cracked or injured, the link rod itself will be damaged or loose the strength due to a stress concentration to such a cracked or injured portion.